(a) Field of the Invention
This invention relates to focal plane shutters for photographic cameras and more particularly to improvements in a focal plane shutter wherein shutter blades consist of a plurality of opaque thin plates.
(b) Description of the Prior Art
In a focal plane shutter of a type wherein shutter blades consist of a plurality of opaque thin plates, such opaque thin plates are pivotally supported on a pair of arms rotatably supported respectively at one end on a shutter base plate so that, when these opaque thin plates are folded or unfolded just before an exposure aperture by the rotation of the pair of arms, the exposure aperture may be opened or closed. One of the arms of the pair is pin-slot-connected with a driving member biased by a driving spring so that the pair of arms may be rotated by this driving member. As described above, in this kind of focal plane shutter, the opaque thin plates are pivotally connected with the arms and one of the arms is connected in a pin-slot type with the driving member. Therefore, backlashes are always present at such connecting points. When the shutter is cocked, these backlashes will fluctuate the stationary positions of the opaque thin plates. Such fluctuation will have an undesirable influence on the performance of the shutter and will make it impossible to accurately control the exposure time.
Under such circumstances, in this field, a very high precision is required in working component parts or particularly pins, holes and slots. Therefore, the passing rate of parts in the mass-production is low, a high skill is required in assembling parts and therefore the production cost of products can not help becoming high.
Further, in this kind of focal plane shutter, many comparatively thin small parts are used and therefore the parts are likely to be deformed or broken by a shock or bound at the time of the end of the motion. Therefore, many cushioning devices and bound preventing devices have been already suggested but have functional defects.